The present invention relates to a method of transmitting forces and/or moments between a drivable test stand powered from outside and a test specimen, such as a vehicle.
Vehicle or vehicle component test stands are designated according to their intended purpose such as power test stands, brake test stands, transmission test stands or engine test stands, for example. Common to all these test stands is, that the component or system under investigation is connected to a source of mechanical power and also to means for absorbing power, for instance a DC motor which may be used as a generator as well as a drive motor. In cases where the DC motor is used as a generator, the drive system functions as a brake for the forces and moments that emanate from the engine of the component or the engine of the vehicle being investigated. In cases where the DC motor functions as a motor, forces and moments are transferred from the motor to the vehicle drive system.
In order to transfer these forces, an interconnection must be created between the driving or braking machine of the test stand and the motor vehicle and/or other component. Such interconnection enables investigation of the forces and moments which occur during investigation of the vehicle or other component.
Heretofore such interconnection has been accomplished by one or several rolls on which the motor vehicle rests. The rolls are driven, for instance by the wheels of the vehicle, and in turn the rolls drive a DC motor functioning as a generator.
This combination is based on friction and results in many disadvantages. One such disadvantage is that the roll diameters must be different according to the power to be transmitted. The roll diameter or diameters on which the driven wheels of the motor Vehicle rest, must be larger with increasing power, speed and duration of the test. Also, in transmission test stands the power to be measured is that which is transmitted to the road by the vehicle motor transmission, driveshaft and rear axle. Often this power train through its drive axles and wheel axles are connected to drive shafts rather than wheels which in turn are connected to drive/brake means for instance a DC motor.
As means for powering or braking the test stand, hydraulic machines or eddy current brakes may be used instead of electric motor. In transmission test stands, however, the power transmission characteristics which are present with roll test stands are missing. Therefore, additional, partially empirically determined correction factors must be considered and these factors are contained in a control device which simulates vehicle driving resistances such as roll resistance and/or air resistance. This is necessary in order to obtain representative conclusions as to the actual usage conditions of the motor vehicle traveling over the road from the data measured on the test stand.
From German Offenlegungsschrift 3,114,714 an apparatus is known for the testing of wheels of motor vehicles under simulated service conditions whereby the vertical forces and the lateral forces are introduced to the vehicle wheels in a service-like manner by means of servo hydraulic cylinders and by means of a loading device. The vehicle wheel with mounted tire is almost harnessed in a rotatable wheel retainer. Such an apparatus serves the purpose of testing the dynamic characteristics of motor vehicle wheels.